An overlock sewing machine is provided with a plurality of loopers. It is necessary to thread each of the loopers with respectively different looper threads, and threading operations were troublesome.
Patent Literature 1 discloses a device for threading a thread to a hollow looper point using compressed air.
According to the device disclosed in Patent Literature 1, when a threading enabled phase is detected and the phase is to be maintained, it is necessary to simultaneously perform operations of pressing a fixing button and operations of rotating a thread take-up lever, so that the operations have needed by means of using both hands.
Moreover, according to the device disclosed in Patent Literature 2, the device has a push button including a control pin and a control groove cam portion receiving the control pin, wherein a user become possible to operate the push button, the control groove cam portion and a main shaft respectively by means using one hand.
On the other hand, in the device of Patent Literature 2, a user become possible to operate by means using one hand, and a user need to operate another return lever for releasing the threading state. Accordingly, a user needs to operate two operating members for performing switching between two modes, so that user-friendliness is poor.